Aero Blasters Sound Test
Activate the Extra Credits code, then press Select at the title screen to access a sound test menu.

Aero Blasters Level Select
Activate the Extra Credits code, then press Button I 10 times to start at level 2. To start at higher levels, Press button I once more for each level above 2. (i.e., 11 times to start on level 3, 12 times for level 4, etc.) To complete the code, press Select, Select, Run.